In normal cutting tool sharpening it was common to use jigs to hold the tool to be sharpened at a predetermined angle to a large water-cooled grind stone. These grinding jigs usually comprised a roller which supported a plate upon which the tool was secured and by which the tool was held at a selected angle against the stone surface. Both the roller and tool were held against the grind stone and as the stone was moved the cutting edge was ground to the selected angle.
It will be evident that the successful use of such jigs were predicated upon the human skill of the artisan. Examples of such jigs are illustrated in Marples Catalogue of Tools, published 1909, #7314; Millers Fulls Company Catalogue 1915, p. 159, #569; Dictionary of Tools, R. A. Salaman, Scribners Inc., 1975, p. 215, 216, and as will be evident the initial setting of the tool in the jig is critical to the success of the operation.
The present use of such guides is now customarily limited to flat bench stones since power stones are not large enough in diameter and knowledge of their use has in major part been lost.
The skilled artisan differentiates between grinding and honing with "grinding" being considered as defining the basic edge and "honing" as refining the basic edge to the finished sharp edge.
In the normal sharpening process the edge to be sharpened is initially passed over the coarse stone at a selected angle, the "bevel angle". This process leaves a ragged edge of the desired angle. The bevel is then refined over a stone of finer particles and since such stones cut more slowly the work is done on that part of the bevel which intersects with the face of the tool to provide a micro-bevel.
Usually, a tool with a bevel of 25.degree. will have a micro-bevel of 5.degree. making a total angle of 30.degree.. The micro-bevel selected should be a function of the tool material, the material to be cut and the intended use. Ideally the bevel angle should be no greater than is necessary to prevent the edge from breaking down so that the wedging action of the tool is minimized as the edge enters the material to be cut.
At present the micro-bevel angle differs from the basic bevel angle by about 5.degree., i.e. when the basic bevel angle is 25.degree. the micro-bevel is 30.degree.. As mentioned previously, smaller differences are preferred but they are not feasible because it has not been possible to set both bevels and micro-bevels consistently. Furthermore, it has not been possible to set lesser micro-bevels with any consistency.